The Global Atmospheric Electric Circuit

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1 The Global Atmospheric Electric Circuit Colin Price Department of Geophysics and Planetary Sciences Tel Aviv University Israel

E-field of ~100 V/m pointing downward Why do we

2 Historical Background 1752 Lemonnier discovered that in fair weather regions there is a persistent E-field of ~100 V/m pointing downward Why do we not get electric shock? (200 V between head and ground)

3 1920s: There exists a diurnal variation of the atmospheric electric field, which is independent of location and local time, but dependent only on universal time: ~100V/m Carnegie Curve

5 Long Term trends in surface Potential Gradient (E)

6 Implication of E-field Earth has a negative charge of ~500,000 C Charge of the Earth Q = 4 πr 2 ε o E = R 2 E o / k = 4.5 x 10 5 Coulomb ε o = permittivity of free space (electric const.) = 8.85x10-12 F/m ,000 Coulombs

7 1887 Linss discovered ions in the atmosphere, implying that air had a finite conductivity The conductivity of the atmosphere is determined by the concentration of ions in the atmosphere. The amount of ions increases with altitude since the main source of ionization is cosmic and solar radiation from outside the Earth's atmosphere. The mobility of ions increases with decreasing density. 100km Ionosphere

8 σ x E j = σ E Conduction Current

9 1900 CTR Wilson measured the air-earth current which has a value ~2x10-12 A/m 2 Conduction Current J(R) = o E(R) = 2 x Amp/m 2 σ(r) =σ o = 3x10-14 Siemen/m [S/m] {1 S = Ω -1 } The conduction current varies little with altitude up to z~50 km Globally, i = J(R) 4πR 2 ~ 1000 Amp

10 Due to the high conductivity of the Earth, the Earth-ionosphere represent a spherical capacitor (i) ~10-5 S/m (o) ~1 S/m (air) ~10-14 S/m Earth ionosphere However, because of the ions in the atmosphere, the capacitor discharges slowly (leaky capacitor) Volt Meter ions

11 Ionospheric Potential The potential difference between the ionosphere (height h) and the Earth s surface, known as the ionospheric potential, is : R+h V = - E(r)dr = - E(r)dr R since E=0 for r> R+h (or z>h). R ionosphere ground Vi Most measurements show values of V~ 3x10 5 Volt (300kV) Resistance of Atmosphere (fair weather) From here we can also see that the total resistance between the Earth and ionosphere is R Ω = V/i = 3x10 5 /1000 ~ 300 Ω

14 Capacitance of the Earth C = Q/V ~ 4x10 5 C/3x10 5 V ~ 1 Farad The typical time scale for the discharging of the capacitor is τ = R Ω C = 300 sec! (5-10 minutes) Conclusion: Without a source of charging of the Earthionosphere capacitor, the charge on the Earth would decay nearly immediately (few minutes). What is the source of this atmospheric charging? What is the battery in circuit? + -

15 1920 Wilson suggested the generator was global thunderstorms 1929 Whipple showed that the diurnal variations of the fair weather field matches the diurnal variations of global thunderstorms

16 The Global Atmospheric Electric Circuit 300 kv 300Ω + - Q ~ -500,000 C PG ~ -100 V/m I ~ 2 pa/m 2 DC Direct Current Global Circuit

17 Rycroft et al. (2000)

18 Where are the batteries? ~1000 thunderstorms

19 Latitudinal Distribution Diurnal Distribution Longitudinal Distribution

24 There is also an AC component to the Global Electric Circuit flashes per second Generation of EM waves Trapped in Earth-ionosphere waveguide

26 Standing Waves Frequency= nv L (Hz) Bell 1 Bell 2

27 ELF- Schumann Resonances Extremely Low Frequency (ELF) Range F < 100 Hz (Schumann, 1952) f n ~ nc 2 a ~ 8, 14, 20. Hz

28 ELF Waveguide Cutoff

29 F ~ n c 40,000km Schumann Resonance Modes 1 and 2 Lightning Discharge Earth Ez 8 Hz Hx,y ELECTRIC FIELD Ionosphere MAGNETIC FIELD Ez 14 Hz Hx,y

30 Theory E r M i ( 1) 2n 1 P cos n 2 n n 1 ( 1 c 4 0 ha ) n 0 H M c 1 2n 1 P n cos n n 1 ( 4 ha n 1 1) ω = angular frequency Θ = great circle angle from lightning to the observer ε 0 = vacuum permittivity; a = radius of the Earth; h = the height of the Ionosphere; P n (cos θ) and P n1 (cos θ) are Legendre and associated Legendre functions of degree n and order 0,1 respectively, the modal eigenvalue related to the propagation constant of the Earth-Ionosphere spherical-shell cavity M c (ω) is the vertical charge moment of the lightning ground flash.

31 f=8 Hz 14 Hz 20 Hz 26 Hz F ~ n c 40,000km (Schumann, 1952)

32 Electric Field Detector NS Mitzpe Ramon EW Magnetic Field detectors

Power (Relative Units) Magnetic Field Amplitude (Volts) Israel SR Amplitude California SR Amplitude 2 1 Time Series 0.7 0.6 r=0.9 0.65 0.6 0-1 -2 0.5 0.4 0.3 0.55 0.5 0.45 0.

33 Power (Relative Units) Magnetic Field Amplitude (Volts) Israel SR Amplitude California SR Amplitude 2 1 Time Series r= Time (seconds) Julian Day Hz Spectrum 14Hz 8 Negev Desert Israel Hz 27Hz 33Hz 39Hz Frequency (Hz)

34 4pm 4pm 4pm

35 Huge Range of Horizontal and Vertical Scales Rycroft and Harrison (2011)

36 Huge range of Temporal Scales Rycroft and Harrison (2011)

37 Global Circuit and Climate Change T

38 Williams (1992) Schumann Resonance Tropical Temperature Anomaly

Magnetic Field Intensity (au) 1800 UT Lightning Activity over South America (SR relative magnitude) 1800 UT Surface Temperature over South America (K) Africa 0.

39 Magnetic Field Intensity (au) 1800 UT Lightning Activity over South America (SR relative magnitude) 1800 UT Surface Temperature over South America (K) Africa S. America Ts SR r= Temperature (K) /11/98 16/11/98 30/11/98 14/12/98 Date Price and Asfur (2006)

40 Upper Tropospheric Water Vapour

41 Upper Tropospheric Water Vapour

42 African Lightning Activity (SR Magnetic Field) Specific Humidity (kg/kg) Lightning Activity vs. Specific Humidity (300mb) +24hours 26% SR change => 0.1 g/kg change r= Day from 20 October 1998 Price and Asfur (2006)

43 Atmosphere Nuclear Testing Harrison (2002) Solar Influences on the Global Circuit Harrison and Usoskin (2010) DC Circuit

sd Bz (nt) -2 0 2 4 6 8 10 0 1 2 3 4 5 6 dbz (nt) -20-10 0 10

44 sd Bz (nt) dbz (nt) October 2011 Bz of IMF from ACE Jz SD of GEC in Israel Year day ACE Bz SD of IMF from ACE Jz Year day Jz SD of GEC in Israel

45 Satori et al. (2005) AC Circuit

46 Hz Hz Frequency of first SR mode (~7.8Hz) X ray flux (W/m^2), log. scale Hz 7.90 Monthly mean values Monthly averaged Frequency for NS and EW components Hew Hz 7.75 NS EW Hns יולי- 05 ינואר- 05 יולי- 04 ינואר- 04 יולי- 03 ינואר- 03 יולי- 02 ינואר- 02 יולי- 01 ינואר- 01 ינואר- 00 יולי- 00 יולי- 99 ינואר- 99 יולי- 98 ינואר- 98 יולי- 97 ינואר- 97 יולי- 96 ינואר- 96 Month/Year 2006 NS, EW frequencies (yearly averaged) Annual Mean Values (SR and X-rays) NS and EW frequencies with Log. ( X Ray Flux (1-8A)), R(NS,1-8A)=0.941, R(EW,1-8A)= r=0.941 r= y = x y = x NS EW Linear (NS ) Linear (EW ) NS EW X rays (0.5-4 A) X rays (1-8 A) X ray flux (W/m^2), log. scale

01/01/2005 08/01/2005 15/01/2005 22/01/2005 29/01/2005 05/02/2005 12/02/2005 19/02/2005 26/02/2005 05/03/2005 12/03/2005 19/03/2005 26/03/2005 01/01/2005 08/01/2005 15/01/2005 22/01/2005 29/01/2005

47 01/01/ /01/ /01/ /01/ /01/ /02/ /02/ /02/ /02/ /03/ /03/ /03/ /03/ /01/ /01/ /01/ /01/ /01/ /02/ /02/ /02/ /02/ /03/ /03/ /03/ /03/2005 Hz SSN Hz X ray flux (W/m^2), log. scale 27-day solar rotation effects on SR frequency SR Spectral Power Variation f 1 =8 Hz f 2 =14 Hz 30day January-March 2005 [Füllekrug and Fraser-Smith, 1996] 7.95 NS frequency (SAO) and X Rays (background flux) 01-03,2005 Hns freq. and SSN NS Freq. av SSN (Belgium) av NS frequency (SAO) and X Rays background, 01-03, 2005 Hns freq. and X-rays NS Freq. av Log Xrays, av Day Day

48 15/10/03 20/10/03 25/10/03 30/10/03 4/11/03 9/11/03 18:00 18:30 19:00 19:30 20:00 20:30 21:00 21:30 22:00 22:30 23:00 23:30 Freq. X - rays W/m^2 pt 15/10/03 20/10/03 25/10/03 30/10/03 4/11/03 9/11/03 Freq. X - rays 15/10/03 20/10/03 25/10/03 30/10/03 4/11/03 9/11/03 Freq. X - rays Ez, 8 Hz, Goes 10-8A, 4A E E E E-07 Freq. 8Hz Goes 10 X rays 8A Goes 10 X rays 4A Solar Flares - X rays 15 Oct-15 Nov E E-09 8Hz Day, 2003 Ez, 14 Hz, Goes 10-8A, 4A E E E-06 Freq. 14Hz Goes 10 X rays 8A Goes 10 X rays 4A E E E-09 14Hz Day, 2003 X Rays and NS Ampl, PKD, 04/11/03 X-rays: Ampl. Ez, 20 Hz, Goes 10-8A, 4A 1.00E+00 9E E E-01 8E E E-06 Freq. 20 Hz Goes 10 X rays 8A Goes 10 X rays 4A 1.00E E-03 7E-10 6E-10 5E E E-04 4E E E-05 3E E-09 20Hz 1.00E-06 Time 2E-10 Day, 2003

49 What do all these changes mean? Changes in thunderstorms? Changes in waveguide? Changes in conductivity?

50 Solar Cycle in Thunderstorm Frequency? Data from (Brooks, 1934) Stringfellow (1974) showed similar relationships for UK from (4 solar cycles)

51 European Thunderstorms (Austria and Germany) Data from ground networks April-September Schlegel et al. (2001)

52 27-day Periodicity in Clouds Global Lightning Clouds Takahashi et al. (2009)

54 What have we learned? The global atmospheric electric circuit is made up of both a DC component and AC component The DC circuit depends on global thunderstorm activity (area coverage, intensity) and atmospheric conductivity (ions, aerosols) The AC circuit depends on global lightning activity (intensity and number of flashes) and ionospheric parameters (D-layer reflection height, ionospheric conductivity profile) There is evidence that solar variability (solar cycle, solar rotation, solar flares) influence both DC and AC circuit parameters These Solar impacts may result from changes in the Earth-ionosphere cavity, and/or even changes in cloud and thunderstorm activity itself. The GEC may also be a sensitive tool to study climate change.

Introduction to the physics of sprites, elves and intense lightning discharges

Introduction to the physics of sprites, elves and intense lightning discharges Michael J. Rycroft CAESAR Consultancy, 35 Millington Road, Cambridge CB3 9HW, and Centre for Space, Atmospheric and Oceanic